In copending applications Ser. No. 812,479, filed July 5, 1977 by Daniel M. Cap and William H. Lake, entitled Higher Pressure Metal Vapor Discharge Lamps Improved in Efficiency, and Ser. No. 845,738, filed Oct. 26, 1977 by Elmer G. Fridrich, titled Miniature High Pressure Discharge Lamps, both assigned like this application, useful and efficient high pressure discharge lamps are disclosed having much smaller sizes than have been considered practical heretofore, namely discharge volumes of 1 cubic centimeter or less. In preferred form achieving maximum efficacy, these high intensity lamps utilize generally spheroidal thin-walled arc chambers together with vapor pressures above 5 atmospheres and reaching progressively higher levels as the size is reduced. The convective arc instability usually associated with the high pressures utilized is avoided and there is no appreciable hazard from possibility of explosion. Practical designs provide wattage ratings or lamp sizes starting at about 100 watts and going down to less than 10 watts, the lamps having characteristics including color rendition, efficacy, maintenance and life duration making them suitable for general lighting purposes.
In order to have high efficacy with a miniature metal vapor lamp, it is necessary for its electrodes to attain the required temperatures for good electron emission even at the low energy inputs involved. An important factor in achieving this result is reduction of the physical size of the electrodes and inleads in order to reduce the heat loss from them. In copending application Ser. No. 824,557, filed Aug. 15, 1977, by Richard L. Hansler, titled "Electrode Inlead for Miniature Discharge Lamps", now U.S. Pat. No. 4,136,298, January 1979, a small size electrode inlead assembly is described comprising a small tungsten pin joined on axis to a fine molybdenum wire having a foil portion for sealing through fused silica. The join in that assembly is effected by a laser butt weld which permits a symmetric compact seal making possible a very small discharge envelope having minimum end losses.